This proposal will examine the mechanism of developmental control of the response of macrophages to the soluble factor interferon-gamma (IFN-g). Mononuclear phagocytes are potent effectors of the immune response against neoplasias. IFN-g, a T-cell derived cytokine, is a potent stimulator of macrophage (MP) function, including tumor cell killing activity. However, MP exhibit a wide range of microheterogeneity, which likely plays a role in the diverse functional differences exhibited by this population of cells. We have shown that not all MP respond similarly to IFN-g stimulation. For example, the murine myelomonocytic cell line. WEHI-3, exhibits a less mature phenotype and fails to develop tumoricidal function after stimulation with IFN-g. However, this is not due to unresponsive cells since WEHl-3 cells do respond to stimulation as is evidenced by the upregulation of the MHC class II I-Aalpha component after IFN-g treatment. In this proposal, we outline an examination of the underlying mechanisms for this differential response to activation by IFN-g. Primary murine bone marrow-derived MP and the WEHI-3 cell line will be used as MP populations for in vitro differentiation by chemical and cytokine treatment. The nature of the IFN-g response before and after differentiation will then be characterized at the level of gene expression and functional activity. The molecular basis of the differential IFN-g response in the immature versus the mature bells will be determined by using electrophoretic mobility shift assays and immunoprecipitation to examine specific transcription factors and signaling proteins utilized in each case. The results of these studies will determine the effect of MP development on the activation response of these cells.